diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 4b48ae1e260..f5ee929c56e 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.86 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.87 2007/08/31 23:35:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -219,7 +219,9 @@ clauselist_selectivity(PlannerInfo *root,
 				s2 = rqlist->hibound + rqlist->lobound - 1.0;
 
 				/* Adjust for double-exclusion of NULLs */
-				s2 += nulltestsel(root, IS_NULL, rqlist->var, varRelid);
+				/* HACK: disable nulltestsel's special outer-join logic */
+				s2 += nulltestsel(root, IS_NULL, rqlist->var,
+								  varRelid, JOIN_INNER);
 
 				/*
 				 * A zero or slightly negative s2 should be converted into a
@@ -702,7 +704,8 @@ clause_selectivity(PlannerInfo *root,
 		s1 = nulltestsel(root,
 						 ((NullTest *) clause)->nulltesttype,
 						 (Node *) ((NullTest *) clause)->arg,
-						 varRelid);
+						 varRelid,
+						 jointype);
 	}
 	else if (IsA(clause, BooleanTest))
 	{
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 60da08b1ec4..ad9f662b68d 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.235 2007/08/21 01:11:18 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.236 2007/08/31 23:35:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1385,11 +1385,24 @@ booltestsel(PlannerInfo *root, BoolTestType booltesttype, Node *arg,
  */
 Selectivity
 nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
-			Node *arg, int varRelid)
+			Node *arg, int varRelid, JoinType jointype)
 {
 	VariableStatData vardata;
 	double		selec;
 
+	/*
+	 * Special hack: an IS NULL test being applied at an outer join should not
+	 * be taken at face value, since it's very likely being used to select the
+	 * outer-side rows that don't have a match, and thus its selectivity has
+	 * nothing whatever to do with the statistics of the original table
+	 * column.  We do not have nearly enough context here to determine its
+	 * true selectivity, so for the moment punt and guess at 0.5.  Eventually
+	 * the planner should be made to provide enough info about the clause's
+	 * context to let us do better.
+	 */
+	if (IS_OUTER_JOIN(jointype) && nulltesttype == IS_NULL)
+		return (Selectivity) 0.5;
+
 	examine_variable(root, arg, varRelid, &vardata);
 
 	if (HeapTupleIsValid(vardata.statsTuple))
diff --git a/src/include/utils/selfuncs.h b/src/include/utils/selfuncs.h
index f0c6f20427c..fc409d9bddd 100644
--- a/src/include/utils/selfuncs.h
+++ b/src/include/utils/selfuncs.h
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/selfuncs.h,v 1.39 2007/01/22 20:00:40 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/selfuncs.h,v 1.40 2007/08/31 23:35:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -149,7 +149,7 @@ extern Datum icnlikejoinsel(PG_FUNCTION_ARGS);
 extern Selectivity booltestsel(PlannerInfo *root, BoolTestType booltesttype,
 			Node *arg, int varRelid, JoinType jointype);
 extern Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype,
-			Node *arg, int varRelid);
+			Node *arg, int varRelid, JoinType jointype);
 extern Selectivity scalararraysel(PlannerInfo *root,
 			   ScalarArrayOpExpr *clause,
 			   bool is_join_clause,